The continuing trend toward reduction in the sizes of micro-electronic devices and towards the provision of increasing numbers of electrical functions on a single integrated circuit chip has required the producers of electrical connectors for connecting conductive pads on chip carriers to conductive pads on circuit boards to correspondingly reduce the size of their connectors. It is, however, always necessary in the design of an electrical connector to provide some minimum contact force at the electrical interfaces between the terminals in the connector and the conductors on the chip carrier and on the circuit board. These contact forces are maintained by providing the terminals in the connector with an integral spring means which forces the contact areas of the terminal against the contact pads on the chip carrier and on the circuit board.
The extremely small size of present day micro-electronic devices and the close spacing of the terminal pads on the chip carrier and on the circuit board necessitates the use of relatively thin metal stock for the terminal in the connector and in order to obtain the required contact forces, designers have increasingly been resorting to the use of terminals having relatively long springs, that is, springs which are part of the terminal and which may extend sinuously from the chip carrier to the circuit board in order to obtain adequate contact forces at a reasonably constant or low spring rate over a relatively wide deflection range. In conventional connectors, the current flowing from the chip carrier to the circuit pad must flow through the spring and because of the length of the spring, self-inductance effects become significant in the connector. The self-inductance in the terminals of the connector give rise to problems, in that it tends to increase the power requirements of the circuit and thereby complicate the heat dissipation and signal propagate problems.
These self-inductance effects are always present in electrical circuits and are often important in conventional solid state micro-electronic circuits containing IC devices with extremely short switching and rise times. The self-inductance effects are particularly significant in circuits operating under cryogenic conditions, such as Josephsen junction devices operating at near zero degrees K. Devices of this type have a switching time on the order of a picosecond. With signals of such short duration, the energy loss which results from even minor self-inductance effects may make the device unusable.
The present invention is directed to the achievement of a connector for connecting first conductors to second conductors which gives the designer freedom to achieve the desired spring characteristics in the terminals of a connector without accompanying self-inductance in the terminals. In accordance with the principles of the invention, each terminal in the connector comprises first and second contact portions which are engageable with a first and second conductor respectively, and which are adjacent to each other. First and second bypass contact surfaces are provided on the contact surfaces and when current flows from the first conductor to the second conductor, it flows from the first conductor to the first contact portion, past the bypass contact surfaces to the second contact portion and then to the second conductor. Contact forces are maintained by an integral spring loop which extends circuitously from the first contact portion to the second contact portion and which, in use, is deflected so that it maintains the necessary contact forces between the conductors and the contact portions of the terminal and at the bypass contact interface. Little, if any, current flows through the spring loop and the inductance effects are thereby minimized or eliminated. The principles of the invention will find application in all circuits in which self-inductance effects may be significant. As mentioned above, the use of the invention is particularly beneficial in circuits having extremely short switching times, such as Josephsen type junction device circuits operating at near zero degrees K.